Background : Carers of people with a severe mental illness often experience health and social problems themselves. In the UK, carers now have a statutory right to an assessment of their needs. Aim : to develop a brief instrument to identify and measure the experience of those caring for people with a severe mental illness across the range of domains that the carers themselves consider important. Method : potential domains were identified from published and 'grey' literature and refined through consultation with carers. Pilots and field trials of the resulting draft instrument involved a total of 412 carers. Results : a self-rated, 13-item questionnaire. Principal components analysis yielded factors relating to impact of caring and the quality of support provided for carers. Test-retest reliabilities for all items were moderately good or better. The great majority of 75 carers, who gave structured feedback, found they could follow the instructions for the instrument and 90% thought the length was 'about right'. Conclusions : CUES-C could be used as part of the carers' assessment. The instrument does cover the domains that carers value, is acceptable to carers and has reasonable test-retest reliability.